Johns Hopkins researchers have devised a way to use a
brief burst of electricity to release biomolecules and
nanoparticles from a tiny gold launch pad. The technique
could someday be used to dispense small amounts of medicine
on command from a chip implanted in the body. The method
also may be useful in chemical reactions that require the
controlled release of extremely small quantities of a
material.

The technique was described Sept. 10 in a presentation
by Peter C. Searson, a professor of
materials science and
engineering in the Whiting School, during the 232nd
national meeting of the American Chemical Society in San
Francisco. "You can think of the useful biomolecule or
nanoparticle as a balloon tethered to a surface," he said.
"We use an electrical pulse to cut the tether, and it
floats away."

This method could be used to control the release of
drug molecules; nanoparticles; biopolymers such as
peptides, proteins and DNA; and protein assemblies such as
viruses, said Searson, who also is director of the
Institute for
NanoBioTechnology at Johns Hopkins.

"The technique is relatively simple, but nothing like
this has been done before," he said. "Scientists have known
that molecules could be removed from a surface in this way,
but it's never been considered useful. They've been more
interested in preventing this from happening."

Yet Searson and
biomedical engineering graduate students Prashant Mali
and Nirveek Bhattacharjee concluded that this controlled
release of molecules might have important applications in
the growing field of nanobiotechnology.

For their experiments, the researchers used gold
electrodes, each as thin as a single strand of human hair,
fabricated through the same photolithography techniques
used to make computer chips. "We used a gold electrode
because gold is a good conductor of electricity," Mali
said, "and, because it's an inert metal, it wouldn't get
involved in any of the chemical reactions."

To tether each useful molecule to this surface, the
team used a long chain of hydrocarbon molecules. At one
end, the tether was anchored to the electrode by a
gold-sulfur bond; at the other end was the biomolecule they
wished to release on command. The researchers then sent a
brief mild pulse of electricity through wires attached to
each electrode. The current caused the bond between the
sulfur atoms and the gold platform to break, setting free
the tethered molecule.

In theory, the researchers said, this technique could
be incorporated into a biocompatible implant chip that
would release medicine inside a patient on command.

Scientists elsewhere are working on other new drug
delivery techniques such as microfabricated containers that
unload their medication inside the body when a lid
dissolves. Although it requires further research and
development, the Searson team's approach could have several
advantages over the container technology. "Because our
molecules are attached to a surface, we can work with much
smaller concentrations," Searson said. "We've also shown
that our system is reusable. After a group of molecules is
released, you can easily attach new molecules to an
electrode and use it again."

Earlier this year, Searson, Mali and Bhattacharjee
reported on their technique in the journal Nano Letters. A
patent on the process is pending, and licensing inquiries
are being handled by the Johns Hopkins Technology Transfer
staff.